Linter (cmd/jennifer/lint.go, internal/lint)

jennifer lint <file.j> reports patterns that are compile-legal but stylistically or semantically suspect - the slot between fmt (which normalises lexical shape) and the parser (which rejects the outright illegal). The checks live in internal/lint; the subcommand in cmd/jennifer/lint.go wraps them with file I/O, config resolution, and output rendering.

The check set is grouped by concern, each check with a stable ID so suppression and configuration stay portable and greppable. The leading digit is the group: L0nn source errors (the file doesn’t parse, or a directive is malformed), L1nn correctness, L2nn complexity and style, L3nn API lifecycle.

The L0nn source errors are always on and not user-selectable: they are produced by the pipeline (lex / preprocess / parse) or the suppression pass (L004), not by an AST walk, so --checks can’t enable or exclude them and they carry a nil run. registry in lint.go marks every other check selectable; selectableIDs() is what --checks resolves against, KnownIDs() (all IDs) is what directive/config validation checks against. Adding a check takes the next free number in its group; a new group (say L4nn for a portability family) is a new leading digit.

Traversal. The parser exposes no generic visitor, so internal/lint carries two: a flat walker (walk.go) with list/stmt/expr hooks for checks that match node shapes (L102/L103/L201/L202/L105), and a scope-aware traversal (scope.go) mirroring the resolver’s frame model for the checks that need binding visibility (L101/L104). Both descend into SpawnExpr.Body, which the resolver deliberately skips: a read inside a spawn still marks an outer local used, but a declaration inside a spawn is left unreported (the resolver’s spawn carve-out, which the linter inherits). The linter runs on the parsed AST alone - it does not call parser.Resolve, so it can lint code that would fail resolution, and it tracks its own bindings and declared types.

Format-honest errors. A lex / preprocess / parse failure is not a stderr bail-out: lintComputeDiags turns it into an L0nn source finding that renders in whatever --format was asked for, so a --format=json pipeline always receives valid output saying why the file couldn’t be checked. stripPositionPrefix peels the FILE:LINE:COL: that the pipeline errors embed, since the finding carries those as fields.

Severity and exit code. A finding at or above SeverityFloor (warning) makes the run exit 1; an info-only run exits 0. Exit 2 is reserved for an invocation failure with no source position - bad flags, unreadable file, or a bad --checks / .jennifer-lint - which prints to stderr. A source error (L0nn, severity error) is a finding, so it exits 1, not 2. Same triaging shape as gofmt -l / shellcheck.

Suppression. # lint-disable: L101 (trailing) silences an ID on that line; # lint-disable-file: L101, L102 silences file-wide. There is no blanket disable-all - a directive names IDs, on the line the finding anchors to (the func line for L201, the block-introducer line for L202). Because the parser strips comments, applySuppressions reads directives off the raw lexer.TokenizeWithFile stream and correlates them to findings by file/line. A malformed or unknown-ID directive is continue-and-report: it becomes an L004 finding, suppresses nothing (so the finding it meant to silence still surfaces), and the run keeps going. A doubled marker (## lint-disable: ...) is an ordinary comment, not a directive.

Selection and suppression are orthogonal layers, and suppression always wins locally: --checks gates which checks run, then applySuppressions filters the findings they produced. So --checks=L203 with a # lint-disable: L203 on one line runs L203 everywhere but silences that one line - suppression can only ever remove findings, never add them, so there is no conflict to resolve.

Configuration. --checks=IDS (per run) or a .jennifer-lint file at the tree root (per project) select checks with one IDS / !IDS direction - all includes (“run only these”) or all excludes (“run everything except”); mixing is an error. Unknown IDs are always an error; naming an always-on L0nn source error in --checks is rejected too. Error messages are terse - unknown check ID "L999", no catalog dump; jennifer lint --help lists the catalog. --format=human|json|github picks the output shape: positioned carets (reusing printErrorContextTo), a JSON array of {id,file,line,col,message,severity} objects, or GitHub Actions annotations. Multi-file --format=json aggregates every file’s findings into one array (a stream of per-file [...] documents would not be valid JSON); human and github stream per file.

TinyGo. The subcommand is build-tag split: lint.go (!tinygo) carries the real implementation and is the only importer of internal/lint, so the whole AST-walking machinery stays out of the jennifer-tiny binary; devtools_tinygo.go (tinygo) stubs runLint to a friendly pointer at the default jennifer binary, alongside the other dev-tool stubs, mirroring the os.run / net pattern.

Part of the CLI reference.